Filter

ABSTRACT

The present invention relates to a filter for liquids. More particularly it is concerned with providing a clog-resistant filter of the kind in which a filter element (usually of hollow cylindrical shape), having at least one open end and with walls of metal, plastic or other suitable material bearing numerous perforations, is placed within a housing in such a manner that the liquid entering the housing must flow from the inside of the filter element out through the perforations in the latter, before it can leave the housing, with the result that solid material strained from the liquid flowing through the filter is retained within the filter element.

BACKGROUND OF THE INVENTION

In "wash filters", the liquid stream input is directed to flow along theinternal face of the filter element. This tends to reduce deposition ofretentions, which are swept to the far end of the filter, where theyaccumulate. Clogging of the perforations is thus delayed. Deflectors soplaced as to accelerate the input flow of liquid along the surface ofthe filter element and thus increase the washing action, are well known.Because of the inevitable drop in the volume of the washing streamcaused by outflow through the perforations, these deflectors are oftenbullet-shaped and designed so as to gradually narrow the annular streamand thus maintain velocity of flow.

The solid material driven to the end of the filter is not completely atrest. Local turbulence, sometimes surprisingly strong, tends to create abackflow, returning some solid material to the main stream, which inturn sweeps it back in a repeating cycle. This process may occur evenwhen the accumulation is in a specially designed recovery zone or driftsinto a sump attached to the housing. Consequently, even if the washingaction along the internal face of the filter element is initiallyefficient in preventing or slowing blockage of the perforations, withtime there is a gradual increase in the concentration of material movingfreely and agitatedly in the liquid flow within the hollow of the filterelement. This increases the chances that retained solids will bedeposited on the surface of the filter element and possibly even forcedinto or through its perforations, leading to a reduction in outputpressure and output flow and to the eventual need for cleaning orreplacement of the filter element.

This problem may be obviated by special, energy-expensive wash filters,as proposed for certain oil and fuel filters (e.g. Verrando, U.S. Pat.No. 2,109,809, Meyer, U.S. Pat. No. 3,622,004), in which the volume offiltrate drawn off through the filter element is a small percentage onlyof the total flow into the filter, the majority of said flow beingcirculated through the filter housing but by-passing the filter elementin a continual cycle incorporating a suitable sump. Such systems require(large and therefore heavy) and expensive filters and pumps, due to thehigh flow rates necessary.

More commonly, the build-up of retentions at the far end of most "washfilters" is flushed out by periodic operation of a manual or automaticvalve. Some of the deposits on the wall of the filter element areexpelled at the same time. These are loosened by the hydraulic shock andthe increased flow within the filter element caused by valve opening. Inmany cases, however, this flushing does not prevent relatively rapidclogging of the filter, as some solid particles wholly or partiallyembedded in the filter element are not dislodged by this operation.

In U.S. Pat. No. 3,862,035, the current inventor disclosed a means forminimizing the accumulation of free or deposited solids in a filter, bycontinually removing from the filter the solids, without interruptingthe flow of liquid through the filter. This prevents or minimizeshydraulic pressure loss and the costs of filter shutdown and cleaning,and for investment in backup. Generally, the latter invention comprisedpressure-reducing means ("bleed") in communication with the filter body,the said bleed continuously discharging a small portion of the liquidflowing through the filter together with solids retained by the filterelement, at a pressure substantially less than that within the filter.Various embodiments of the invention have greatly increased the workingcycle of filters. They have also improved quality of filtration, bylessening eventual penetration through the filter element perforationsof solids previously retained, though smaller than, or similar in sizeto the perforations, and of even larger solids, worn down by repeatedparticle-particle and particle-filter elements impacts, the lattercaused by turbulence in the hollow of the filter element. Despiteconsiderable improvements in performance and operational convenienceprovided by the latter invention for most liquid and particularly forwash filters, a number of problems remained.

Even when the load of solids in the liquid stream entering the filterelement is relatively low and it is swept instantaneously to the filterend, turbulence may return some of the solids upstream as described,preventing immediate discharge through the bleed device. Furthermore,even when instant discharge of the bulk of retentions through the bleeddoes take place, there is a small increase in the number of freeparticles circulating indeterminately at the far end of the filter.Consequently, deposition and clogging usually start at the far end ofthe filter element in wash filters, even in those equipped with thebleed device. These processes are speeded when the input of solids tothe filter is relatively heavy, and more so when solids enter in spurts.Increasing the liquid discharge rate through the bleed device is apartial solution, but this may be limited by a need for an economic andpractical ratio between the total flow through the filter and the amountof liquid discharged through the bleed device.

In general, clogging of the filter element depends substantially on theconcentration of retained solids moving around within the filter elementat any given time. This in turn depends mainly on whether the dischargestream from the bleed is sufficient to remove solids swept to itsvicinity. Even when there is a considerable, continual discharge throughthe pressure-reducing bleed, a free particle may not be evicted and thusremain for an extended period within the liquid contents of the filterelement. However, it is useful to consider removal of liquid from withinthe filter element, as if the discharge were periodic and as if thevolume evacuated per discharge was equal to the internal volume of thefilter element (i.e. one Filter Element Evacuation, or one FEE). Thus,if the bleed flow is e.g. 500 liters/hour and the internal volume of thefilter element is 2 liters, on the described theoretical and arbitrarybasis, the liquid contents of said filter element together with retainedsolids, will be discharged 250 times/hour, or about four FEE/minute.

Traditionally, the internal volume of the kind of filter elementreferred to has been dictated by the required hydraulic and filtrationcharacteristics of the filter element. It has not been considered as aparameter independent of the dimensions of the body defining it. Evenwhen solid deflectors have been placed wholly or partly within it, thesehave been designed in relation to the filter screen, usually in order toincrease or maintain the velocity of flow along the latter, or toachieve and maintain desired pressure characteristics through the filterscreen. The extent to which they have reduced the volume of liquidwithin the filter element has been purely incidental.

It is one of the objects of the present invention to overcome thedisadvantages of the prior-art filters and to provide a filter that isoperatable for long periods without clogging.

This, the present invention achieves by providing a filter forseparating solids from liquids, with means for the reduction ofaccumulation of solids within the filter and with automatic means forthe continuous separation and removal at reduced pressure ofliquid-entrained solids during filter operation, comprising:

a housing provided with an inlet for the liquid to be filtered, andprovided with a first outlet for filtrate and with a second outlet forliquid containing a high concentration of solids;

a hollow filter element insertable into said housing, the internal sideof said filter element being in fluid connection with said inlet and theexternal side of said filter element being in fluid connection with saidfirst outlet;

a volume reduction device inserted in said filter element and being of asize to occupy a major portion of the hollow of said filter element;

a pressure reduction device in fluid connection with said second outlet,and provided with discharge means for solids and for the liquid in whichthey are entrained;

whereby said filter may operate for extended periods while clogging ofsaid filter element is inhibited.

The invention will now be described in connection with certain preferredembodiments with reference to the following illustrative figures so thatit may be more fully understood.

With specific reference now to the figures in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

In the drawings:

FIG. 1 is a cross-sectional view of a filter according to a firstembodiment of the invention, wherein the discharge devices for thesolids are shown in schematic form;

FIG. 2 is a fragmented cross-section showing a second embodiment of thevolume reduction device (henceforth VRD);

FIG. 3 is an end view of the VRD shown in FIG. 2;

FIG. 4 is a fragmented cross-section showing a third embodiment of theVRD;

FIG. 5 is an end view of the VRD shown in FIG. 4, and

FIG. 6 is a fragemented cross-section showing a fourth embodiment of theVRD.

There is seen in FIG. 1 a housing 10 made in two parts for convenienceof assembly, containing a hollow cylindrical filter element 12 bearingnumerous perforations, these parts being of conventional design. A VRD14 of substantially cylindrical shape occupies the major portion of theinternal volume of the filter element 12. The housing 10 is providedwith an inlet 16, with a first outlet 18 connectable to a filtratereceptor and a second outlet 20 at the far end of the housing 10. Tofacilitate flow through the inlet 16, one end of the VRD 14 isstreamlined. A passage 22 for fluids and entrained solids provides aconnection between the outer periphery of the VRD 14 and the secondoutlet 20, which outlet is connected to a pressure reducing device 24.This device has been fully described in U.S. Pat. No. 3,862,035. Thedevice 24 has a discharge outlet 28. A sump 26 connected between saidsecond outlet 20 and the inlet of the pressure reducing device 24 mayoptionally be provided. A discharge valve 30 being hand or automaticallyoperable is also connected to the second outlet 20.

FIG. 2 shows a second embodiment of the VRD 14, wherein the end of theVRD 14 facing the second outlet has been provided with a hollow shapedas a spherical segment, this hollow serving as a solid accumulation zoneto enhance the collection of solids. The surface 29 of said housingbounding said zone is provided with several apertures 31 for fluids andsolids flowing towards the second outlet 20.

In a third embodiment of the VRD 14 shown in FIGS. 4 and 5, the end faceof the VRD is provided with twelve radially disposed channels 33, eachpreferably having a cross-section of at least 16 sq. mm, which channelslead to a central depressed chamber 35 positioned opposite outlet 20 forchanneling flow to second outlet 20.

Sump 26 is preferably provided with baffle plates 27 which serve toreduce regurgitation of solids back in the direction of the filter.

FIG. 6 shows a fourth embodiment of the VRD 14, wherein the end facingthe second outlet 20 is streamlined, this providing a zone forcollection of solids. A grooved spider tube 32 serves as a spacerbetween the VRD 14 and the second outlet 20 and allows passage forfluids and entrained solids.

In operation the filter is usually used for obtaining a filtrate free ofsolid contaminants, but it may serve the purpose of recovering ahigh-value solid in some industrial processes. The fluid to be processedis fed into the inlet 16 from where it proceeds along the narrow annularpassage between the outside of the VRD 14 and the inner face of thefilter element 12. The greater portion of the liquid passes through theperforations of the filter element 12 and then out through the firstoutlet 18. Solid particles too large to pass through the filter element12 will either accumulate on the inner face thereof mostly, or will becarried by that portion of the liquid which flows towards the passage 22or through outlet 20 toward the optional sump 26 and the pressurereducing device 24 and then through the discharge outlet 28.

The narrow space between the VRD 14 and the filter element 12 inhibitsrecirculation therein, and consequently there is little opportunity forsolids to accumulate on the inside of the filter element 12.

When processing fluids containing large quantities of solids, even themaximal permissible rate of bleed flow may not be sufficient to preventgradual clogging of the filter element 12. Periodic operation of thedischarge valve 30 causes hydraulic shock in the filter and will usuallyloosen and remove solids caked on the inside of the filter element 12.Valve operation may be manual in response to a perceived reduction infilter output. Automatic methods of valve operation, usually triggeredby a sensed increase of pressure differential across the filter, are, ofcourse, well known.

As will be realized the present invention provides a simple andcost-effective answer to problems not solved by the pressure-reducingbleed device of U.S. Pat. No. 3,862,035 and is a logical adjunct to thelatter. It provides a volume reduction device which is disposed withinthe filter element in such a manner and with such a shape so as tominimize the volume of the liquid between the walls of the device andthe filter element and thus improve the performance of thepressure-reducing discharge device, without significant detriment to thehydraulic qualities.

In the device according to the present invention pressure loss has beenacceptable, even when the internal volume of the filter element has beenreduced by up to 88%. In the example above, this would result in anincrease in FEE number to 35/minute (more than one evacuation every twoseconds), resulting in superior filtration and a greatly increasedworking cycle for the filter, even when the liquid-borne load of solidsinto the filter or separator was great. In some cases, where dailycleaning of accumulated filter deposits had been necessary, use of thesaid device, in combination with continual discharge through a bleeddevice and in some conditions, with additional periodic blow-out througha manual or automatic valve, resulted in working cycles of weeks andeven months without having to cease filtration to clean the filterelement.

The degree of efficiency afforded by the invention, makes itparticularly suitable for liquid and/or solid recovery, in industrialseparations with critical cut-off specifications and/or in continuousprocesses.

Alternatively or additionally to an increased FEE number where the firstpriority is continuous unattended operation, the VRD can be exploited toreduce the bleed discharge to a minimal rate, without reduction infiltration efficiency. This will be desirable in certain circumstances,particularly when the filtered liquid is of high value, as in someindustrial applications.

A hydrodynamic shape is often desirable for bodies exposed to rapidlyflowing liquid medium, but it is not essential for the volume reductiondevice (VRD) of this invention, particularly where filtration efficiencyis of primary concern.

In another embodiment of the invention, the valve may be powered by thesaid pressure-reducing means, when said means is ahydraulically-operated mechanism as described in U.S. Pat. No. 3,862,035the teachings of which are incorporated herein by reference.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrative embodiments andthat the present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be enhanced therein.

What is claimed is:
 1. In a filter for separating solids from liquids,with means for the reduction of the accumulation of solids within thefilter and with automatic means for the continuous separation andremoval at reduced pressure of liquid-entrained solids during filteroperation, The Improvement comprising: means for providing operation ofsaid filter for substantially extended periods of time while inhibitingclogging of said filter, including:a housing provided with an inlet forthe liquid to be filtered, and provided with a first outlet for filtrateand with a second outlet for liquid containing a high concentration ofsolids; a hollow filter element insertable into said housing, theinternal side of said filter element being in fluid connection with saidinlet and the external side of said filter element being in fluidconnection with said first outlet; a volume reduction device inserted insaid filter element and being of a size to occupy a major portion of thehollow of said filter element; a pressure reduction device in fluidconnection with said second outlet, and provided with discharge meansfor solids and for the liquid in which they are entrained.
 2. The filterfor separating solids from a liquid as claimed in claim 1, wherein saidvolume reduction device has a streamlined shape at its end facing saidfluid inlet.
 3. The filter for separating solids from a liquid asclaimed in claim 1, wherein said volume reduction device is providedwith radial grooves at its end facing said second outlet.
 4. The filterfor separating solids from a liquid as claimed in claim 1, wherein saidvolume reduction device is provided with an end facing said secondoutlet, shaped to form a solid accumulation zone bound by said end and asurface of said second outlet.
 5. The filter for separating solids froma liquid as claimed in claim 1, further comprising a manually operateddischarge valve in fluid connection with said second outlet.
 6. Thefilter for separating solids from a liquid as claimed in claim 1,further comprising an automatically operated discharge valve in fluidconnection with said second outlet.